Investment Securities (Components Of Investment Securities) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Schedule of Investments [Line Items]
Agency securities transferred to consolidated VIEs		$ 945		$ 945		$ 1,029
Amortized cost		53,012		53,012		52,147
Total agency MBS, at fair value		54,363		54,363		52,360
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure		$ 54,470		$ 54,470		$ 52,473
Weighted average coupon		3.63%		3.63%		3.63%	[1]
Weighted average yield		2.68%		2.68%		2.78%	[2]
Unamortized Principal Balance Of Interest Only Strips				$ 1,000		$ 1,000
Weighted Average Contractual Interest Rate Of Interest Only Strips				5.29%		5.28%
Unamortized Principal Balance Of Principal Only Strips				$ 192		$ 207
Future Prepayment Rate Assumption Of Investment Portfolio				11.00%		8.00%
Non-Agency Securities Unrealized Gain		$ 2		$ 2		$ 0
Non-Agency Securities Unrealized Loss		0		0		(1)
Mortgage Backed Securities Amortized Cost		53,317		53,317		52,464
Mortgage Backed Securities Unrealized Gain		1,166		1,166		407
Mortgage Backed Securities Unrealized Loss		(13)		(13)		(398)
Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
MBS, par value		50,758		50,758		49,955
Unamortized discount		(33)		(33)		(36)
Unamortized premium		2,287		2,287		2,228
Amortized cost		53,012		53,012		52,147
Gross unrealized gains				1,116		368
Gross unrealized losses				(10)		(395)
Total available-for-sale MBS, at fair value		54,118		54,118		52,120
Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Interest-only and principal-only strips, amortized cost		305		305		317
Gross unrealized gains		50		50		39
Gross unrealized losses		(3)		(3)		(3)
Total MBS measured at fair value through earnings		352		352		353
Fannie Mae [Member]
Schedule of Investments [Line Items]
Total agency MBS, at fair value		$ 43,204		$ 43,204		$ 41,214
Weighted average coupon	[1]	3.61%		3.61%		3.62%
Weighted average yield	[2]	2.67%		2.67%		2.79%
Fannie Mae [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
MBS, par value		$ 40,245		$ 40,245		$ 39,205
Unamortized discount		(30)		(30)		(32)
Unamortized premium		1,766		1,766		1,707
Amortized cost		41,981		41,981		40,880
Gross unrealized gains				897		286
Gross unrealized losses				(7)		(283)
Total available-for-sale MBS, at fair value		42,871		42,871		40,883
Fannie Mae [Member] | Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Interest-only and principal-only strips, amortized cost		288		288		298
Gross unrealized gains		47		47		35
Gross unrealized losses		(2)		(2)		(2)
Total MBS measured at fair value through earnings		333		333		331
Freddie Mac [Member]
Schedule of Investments [Line Items]
Total agency MBS, at fair value		$ 11,103		$ 11,103		$ 11,081
Weighted average coupon	[1]	3.70%		3.70%		3.69%
Weighted average yield	[2]	2.68%		2.68%		2.77%
Freddie Mac [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
MBS, par value		$ 10,356		$ 10,356		$ 10,575
Unamortized discount		(3)		(3)		(4)
Unamortized premium		519		519		519
Amortized cost		10,872		10,872		11,090
Gross unrealized gains				215		80
Gross unrealized losses				(3)		(111)
Total available-for-sale MBS, at fair value		11,084		11,084		11,059
Freddie Mac [Member] | Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Interest-only and principal-only strips, amortized cost		17		17		19
Gross unrealized gains		3		3		4
Gross unrealized losses		(1)		(1)		(1)
Total MBS measured at fair value through earnings		19		19		22
Ginnie Mae [Member]
Schedule of Investments [Line Items]
Total agency MBS, at fair value		$ 56		$ 56		$ 65
Weighted average coupon	[1]	3.08%		3.08%		3.18%
Weighted average yield	[2]	1.95%		1.95%		1.97%
Ginnie Mae [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
MBS, par value		$ 53		$ 53		$ 62
Unamortized discount		0		0		0
Unamortized premium		1		1		1
Amortized cost		54		54		63
Gross unrealized gains				2		2
Gross unrealized losses				0		0
Total available-for-sale MBS, at fair value		56		56		65
Ginnie Mae [Member] | Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Interest-only and principal-only strips, amortized cost		0		0		0
Gross unrealized gains		0		0		0
Gross unrealized losses		0		0		0
Total MBS measured at fair value through earnings		0		0		0
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Investments [Line Items]
Amortized cost		105		105		114
Total agency MBS, at fair value		$ 107		$ 107		$ 113
Weighted average coupon	[1]	3.50%		3.50%		3.50%
Weighted average yield	[2]	3.00%		3.00%		3.33%
Trading Securities, Other		$ 107		$ 107		$ 113
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
MBS, par value		104		104		113
Unamortized discount		0		0		0
Unamortized premium		1		1		1
Amortized cost		105		105		114
Gross unrealized gains				2		0
Gross unrealized losses				0		(1)
Total available-for-sale MBS, at fair value		107		107		113
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Interest-only and principal-only strips, amortized cost		0		0		0
Gross unrealized gains		0		0		0
Gross unrealized losses		0		0		0
Total MBS measured at fair value through earnings		0		0		$ 0
Interest Only And Principal Only Strip [Member]
Schedule of Investments [Line Items]
Unrealized Gain (Loss) on Securities		$ 0	$ (7)	$ 11	$ 4

[1] The underlying unamortized principal balance ("UPB" or "par value") of our interest-only securities was $1.0 billion and the weighted average contractual interest we are entitled to receive was 5.29% of this amount as of June 30, 2016. The par value of our principal-only securities was $192 million as of June 30, 2016.

[2] Incorporates a weighted average future constant prepayment rate assumption of 11% based on forward rates as of June 30, 2016